Investment Securities

The following tables present the amortized costs, unrealized gains, unrealized losses and approximate fair values of investment securities at March 31, 2018 and December 31, 2017:



(in thousands)	March 31, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
AVAILABLE FOR SALE:
U.S. Treasury and agencies	$	40,017	$	—	$	(499	)	$	39,518
Obligations of states and political subdivisions	299,855		3,295		(3,599		)	299,551
Residential mortgage-backed securities and collateralized mortgage obligations	2,682,266		956		(74,877		)	2,608,345
	$	3,022,138	$	4,251	$	(78,975	)	$	2,947,414
HELD TO MATURITY:
Residential mortgage-backed securities and collateralized mortgage obligations	$	3,667	$	1,002	$	—		$	4,669
	$	3,667	$	1,002	$	—		$	4,669



(in thousands)	December 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
AVAILABLE FOR SALE:
U.S. Treasury and agencies	$	40,021	$	—	$	(323	)	$	39,698
Obligations of states and political subdivisions	303,352		6,206		(1,102		)	308,456
Residential mortgage-backed securities and collateralized mortgage obligations	2,703,997		2,039		(40,391		)	2,665,645
Investments in mutual funds and other securities	51,959		11		—			51,970
	$	3,099,329	$	8,256	$	(41,816	)	$	3,065,769
HELD TO MATURITY:
Residential mortgage-backed securities and collateralized mortgage obligations	$	3,803	$	1,103	$	—		$	4,906
	$	3,803	$	1,103	$	—		$	4,906

The above tables reflect that the equity securities are no longer classified as available for sale securities, and instead separately disclosed on the balance sheet. The equity securities were previously reported in investments in mutual funds and other securities within available for sale investment securities.

Investment securities that were in an unrealized loss position as of March 31, 2018 and December 31, 2017 are presented in the following tables, based on the length of time individual securities have been in an unrealized loss position.



March 31, 2018
(in thousands)	Less than 12 Months				12 Months or Longer				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
AVAILABLE FOR SALE:
U.S. Treasury and agencies	$	39,518	$	499	$	—	$	—	$	39,518	$	499
Obligations of states and political subdivisions	92,400		2,058		24,496		1,541		116,896		3,599
Residential mortgage-backed securities and collateralized mortgage obligations	1,309,122		27,267		1,209,663		47,610		2,518,785		74,877
Total temporarily impaired securities	$	1,441,040	$	29,824	$	1,234,159	$	49,151	$	2,675,199	$	78,975



December 31, 2017
(in thousands)	Less than 12 Months				12 Months or Longer				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
AVAILABLE FOR SALE:
U.S. Treasury and agencies	$	39,699	$	323	$	—	$	—	$	39,699	$	323
Obligations of states and political subdivisions	20,566		322		24,798		780		45,364		1,102
Residential mortgage-backed securities and collateralized mortgage obligations	1,184,000		10,368		1,226,364		30,023		2,410,364		40,391
Total temporarily impaired securities	$	1,244,265	$	11,013	$	1,251,162	$	30,803	$	2,495,427	$	41,816

The unrealized losses on the available for sale securities portfolio were caused by changes in market interest rates or the widening of market spreads subsequent to the initial purchase of these securities and are not due to the underlying credit of the issuers. Management monitors the securities within the portfolio, including the published credit ratings of the obligations of state and political subdivisions securities for material rating or outlook changes. As of March 31, 2018, 97% of the obligations of states and political subdivisions securities were rated A3/A- or higher by rating agencies. Substantially all of the Company's obligations of states and political subdivisions are general obligation issuances. All of the available for sale residential mortgage-backed securities and collateralized mortgage obligations portfolio in an unrealized loss position at March 31, 2018 are issued or guaranteed by government sponsored enterprises. It is expected that the mortgage-backed securities and collateralized mortgage obligations securities will be settled at a price at least equal to the amortized cost of each investment.

Because the decline in fair value of the available for sale securities portfolio is attributable to changes in interest rates or widening market spreads and not credit quality, and because the Bank does not intend to sell the securities and it is not more likely than not that the Bank will be required to sell these securities before recovery of their amortized cost basis, which may include holding each security until maturity, these investments are not considered other-than-temporarily impaired.

The following table presents the contractual maturities of investment securities at March 31, 2018:



(in thousands)	Available For Sale				Held To Maturity
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
AMOUNTS MATURING IN:
Due within one year	$	22,399	$	22,267	$	—	$	—
Due after one year through five years	73,780		73,824		—		—
Due after five years through ten years	435,437		429,274		18		19
Due after ten years	2,490,522		2,422,049		3,649		4,650
	$	3,022,138	$	2,947,414	$	3,667	$	4,669

The following table presents, as of March 31, 2018, investment securities which were pledged to secure borrowings, public deposits, and repurchase agreements as permitted or required by law:



(in thousands)	Amortized Cost		Fair Value
To the Federal Home Loan Bank to secure borrowings	$	449	$	448
To state and local governments to secure public deposits	904,227		887,820
Other securities pledged principally to secure repurchase agreements	435,384		422,762
Total pledged securities	$	1,340,060	$	1,311,030